Fixed #21 (#22)

Author: chewxy

atan2.go

@@ -2,6 +2,25 @@ package math32
 
 import "math"
 
-func Atan2(x, y float32) float32 {
-	return float32(math.Atan2(float64(x), float64(y)))
+// Atan2 returns the arc tangent of y/x, using the signs of the two to determine the quadrant of the return value.
+// Special cases are (in order):
+// 	Atan2(y, NaN) = NaN
+// 	Atan2(NaN, x) = NaN
+// 	Atan2(+0, x>=0) = +0
+// 	Atan2(-0, x>=0) = -0
+// 	Atan2(+0, x<=-0) = +Pi
+// 	Atan2(-0, x<=-0) = -Pi
+// 	Atan2(y>0, 0) = +Pi/2
+// 	Atan2(y<0, 0) = -Pi/2
+// 	Atan2(+Inf, +Inf) = +Pi/4
+// 	Atan2(-Inf, +Inf) = -Pi/4
+// 	Atan2(+Inf, -Inf) = 3Pi/4
+// 	Atan2(-Inf, -Inf) = -3Pi/4
+// 	Atan2(y, +Inf) = 0
+// 	Atan2(y>0, -Inf) = +Pi
+// 	Atan2(y<0, -Inf) = -Pi
+// 	Atan2(+Inf, x) = +Pi/2
+// 	Atan2(-Inf, x) = -Pi/2
+func Atan2(y, x float32) float32 {
+	return float32(math.Atan2(float64(y), float64(x)))
 }